The invention relates generally to semiconductor devices and more particularly, to semiconductor devices with conductive bumps and processes for forming them.
Current environment or health issues regarding packaging typically raise concerns with the use of lead. Many of the current flip chip methods that have conductive bumps typically have a relatively high proportion of lead within the bumps. In one particular type of bump called Controlled Collapsed Chip Connection (C4), the bumps typically have approximately 97 weight percent lead and approximately 3 weight percent tin. These bumps cause three different problems. First, they have more lead than many customers like to have. Secondly, a relatively high temperature is needed to flow the bumps, and thirdly, the use of lead typically causes alpha particle generation for the semiconductor device.
In an attempt to reduce the high temperature flow, Evaporated Extended Eutectic bumps (E3) have been used to reduce the flow temperature. In this particular embodiment, a bump typically includes a relatively thin layer of tin under a relatively thick, mostly lead layer, and capped with a relatively thin layer of tin. During the flow process, the tin and lead, at a point distal to the die, flow relatively easily at a temperature no greater than approximately 200xc2x0 C. to make a good chip connection at a relatively low temperature. The problems with the E3 bumps are that they still have too much lead and have problems with alpha particles.
In an attempt to reduce the alpha particle problem, an idea has been generated to use two different types of lead. The lower lead layer has very few impurities and is covered by a typical commercial lead layer. The problem with this is that during the heat and flow, some of the lead and impurities from the commercial layer may migrate to the lower lead layer. Therefore, the alpha particle reduction may not be very significant. Further, it also suffers from the same two problems with the C4 bumps, such as too much lead and too high of a flow temperature.